Curbs on emissions of carbon dioxide and other substances have been strengthened against a background of a growing environmental protection movement, and in the automobile world there is now vigorous development of electric vehicles (EVs) and hybrid electric vehicles (HEVs) alongside vehicles using fossil fuels such as gasoline, diesel oil and natural gas. In addition, the soaring prices of fossil fuels in recent years have acted to spur on the development of EVs, HEVs and the like.
The batteries used for such EVs, HEVs and the like are generally nickel-hydrogen secondary batteries or lithium ion secondary batteries. But what is now being required of such vehicles is not only environmental friendliness, but also basic performance as an automobile—in other words, superior driving capabilities. Therefore it is necessary not simply to enlarge the battery capacity, but also to increase the battery output, which exerts large effects on an automobile's acceleration and hill-climbing performance. However, when a high output is discharged, a large current flows in the battery, and as a result there is an increase in heat-up due to contact resistance between the collectors and the external terminal for the external connection, which are the generation elements. Thus, batteries for EVs and HEVs are required not only to be large-sized and large capacity, but also to handle a large current. Accordingly, many improvements have been carried out with regard to lowering the internal resistance by preventing electric-connection faults between the collectors and external terminal, which are the generation elements.
As a method for electrically joining the collectors and the external terminal, which are the generation elements, mechanical crimping has been frequently used conventionally. However, since only by a simple mechanical crimping, the electrical resistance changes over time under an environment with frequent vibrations, such as with EVs and HEVs, mechanical crimping is used in combination with laser welding. Here, an example for combining mechanical crimping and laser welding as a conventional method for electrically joining the collectors and the external terminal, which are the generation elements, is described referring to FIGS. 6 to 9.
FIG. 6 is a cross sectional view showing a joint of collectors and an external terminal, which are the generation elements disclosed in JP-A-2004-14173, turned upside down. FIG. 7 is a partial cross sectional view showing a joint of collectors and an external terminal, which are the generation elements disclosed in JP-A-Heisei 6-231740. FIG. 8 is an enlarged cross sectional view showing a joint of collectors and an external terminal, which are the generation elements disclosed in JP-A-2003-272604. In addition, FIG. 9 is a cross sectional view showing a joint of collectors and an external terminal, which are the generation elements in FIG. 6 before the welding.
A joint 70 of collectors and an external terminal, which are the generation elements disclosed in JP-A-2004-14173 includes: as shown in FIG. 6, a cover plate 71 fixed to a battery outer body (not shown in the drawings); an inside insulating-sealing material 72 and an outer insulating-sealing material 73; a collector 74 connected to the generation elements; and a rivet terminal 75. The inside insulating-sealing material 72 and the outer insulating-sealing material 73 have a through-bore and are arranged in both inner and outer circumferential parts of an opening formed in the cover plate 71. The collector 74 has a terminal opening and a projected body 74a sagging along the terminal opening, and is arranged superimposed on the inside insulating-sealing material 72. The rivet terminal 75 has a rivet part 75b projection-contacted from a jaw part 75a. 
Then, the joined part 70 is produced by a method including: assembling the rivet part 75b of the rivet terminal 75 so that from the outer circumference side of the cover plate 71, the rivet part 75b penetrates the through-bore of the inside insulating-sealing material 72 and the outer insulating-sealing material 73, the opening of the cover plate 71 and the rivet terminal opening of the collector 74; crimping the rivet part 75b of the rivet 75 by pushing the projected body 74a of the collector 74 thereto; and laser-welding the rivet part 75b and the collector 74 to form a welded portion 76.
In addition, a joint 80 of collectors and an external terminal, which are the generation elements disclosed in JP-A-Heisei 6-231740 includes: as shown in FIG. 7, a resin-made opening-sealing plate 81; a rivet 82; a metal-made washer 83; a washer 84 for attaching a cap; and a terminal cap 85. The rivet 82 includes: a head portion 82a of the rivet having a large diameter; and a foot portion 82c of the rivet having a diameter smaller than that of the head portion 82a and extending perpendicularly from the head portion 82a of the rivet in which an opening portion 82b is formed in a tip portion thereof. In addition, in the resin-made opening-sealing plate 81, a through-bore 81a is formed in the central part thereof, as well as concave portions 81b and 81c for placing respectively the metal-made washer 83 and the washer 84 for attaching a cap thereon are formed respectively around the through-bore 81a on the surface and around the through-bore 81a on the reverse surface.
Then, the joint 80 is produced as follows. First, the foot portion 82c of the rivet 82 is caused to penetrate the through-bore 81a of the metal-made washer 83 and the resin-made opening-sealing plate 81, and further the washer 84 for attaching a cap. Next, the opening portion 82b formed in the tip portion of the foot portion 82c of the rivet 82 is crimped toward the side of the washer 84 for attaching a cap, and then the terminal cap 85 is attached. Thereafter, an appropriate portion of the position 86 between the head portion 82a of the rivet 82 and the metal-made washer 83 is laser-welded to produce the joint 80.
In addition, in a joint 90 of collectors and an external terminal, which are the generation elements disclosed in JP-A-2003-272604, as shown in FIG. 8, to a battery header 91 provided in an upper opening of the battery outer can, a collector 93 connected to a generation element 92 is joined via an aluminum-made electrode delivering pin 94a of an electrode terminal 94. The electrode delivering pin 94a is insulated from a metal plate 91a of the battery header 91 by an outer insulating plate 95 and an inner insulating plate 96 which are fitted in a through-bore provided in a metal plate 91a of the battery header 91. In addition, on the upper surface of the outer insulating plate 95, a nickel-made electrode drawing plate 97 for joining a lead wire for external connection thereto is provided.
Then, by irradiating a laser to a contacted portion of the outer circumference portion 98 formed by crimping the surface of the electrode drawing plate 97 and the electrode delivering pin 94a and the electrode drawing plate 97, the joint 90 composed of nickel and aluminum is formed. Since the joint 90 disclosed in JP-A-2003-272604 is formed by laser-welding a contacted portion of a metal and another different metal having a melting point different largely from that of the former metal in an electrode terminal formed by crimping, the impairment of conductivity connection properties of a contacted surface due to the change with time can be prevented.
As described above, since the continuity of the joint of the collector and the external terminal, which are the generation elements, is produced by crimping the external terminal, that is, only by pressure-welding, the resistance cannot be expected to be thoroughly lowered, so that by laser-welding a crimped portion of the external terminal and the collector which is a generation element, the contact resistance is reduced. However, for example, in a crimping method of a conventional example shown in FIG. 6, as shown in FIG. 9, since the more the tip 75c of the crimped portion after the rivet portion of 75b of the rivet terminal 75 has been crimped, the smaller the material thickness of the rivet portion 75b which becomes spread, a gap 77 is caused between the projected body 74a of the collector 74 and the tip 75c of the crimped portion. Therefore, the welding of the projected body 74a of the collector 74 and the tip 75c of the crimped portion is performed by irradiating a laser beam in a diagonal direction of about 45° with aiming at the gap, by reflecting the laser beam redundantly in the gap and by molten-joining the crimped portion tip 75c and the projected body 74a of the collector 74 to obtain a laser welded portion 76 shown in FIG. 6.
In the laser welding, an assistance gas is used. However, this assistance gas does not circulate thoroughly around the welded portion 76 in the gap, so that spattered metal fine particles during the laser welding are oxidized and soot-shaped metal oxide fine particles are attached to the member to be welded. Moreover, during the production of a battery on an industrial scale, the laser welding of a terminal portion is performed on an assembly line, so that a deviation between the welded portion of the battery and a laser irradiated position is caused sometimes. In this case, when the laser irradiated position is deviated to the side of the projected body 74a of the collector 74, the amount of the laser beam irradiated to the side of the crimped portion tip 75c of the rivet terminal 75 becomes small, so that a melting deficit is caused. On the contrary, when the laser irradiated position is deviated to the side of the crimped portion tip 75c of the rivet terminal 75, the surface of the side of the tip 75c of the crimped portion is spattered, so that the laser welding is not performed normally. Such a phenomenon is caused not only in a conventional example shown in FIG. 6, but also in conventional examples shown in FIGS. 7 and 8 alike.
In addition, since in the above-described conventional examples, the laser irradiation is performed in a direction diagonal relative to the member to be welded, in order to weld multiple positions symmetrically, the member to be welded is necessary to be rotated, there is a problem that the production apparatus becomes complex.